Mechanical couplings for joining pipe elements together end-to-end comprise interconnectable segments that are positionable circumferentially surrounding the end portions of co-axially aligned pipe elements. The term “pipe element” is used herein to describe any pipe-like item or component having a pipe-like form. Pipe elements include pipe stock, pipe fittings such as elbows, caps and tees as well as fluid control components such as valves, reducers, strainers, restrictors, pressure regulators and the like.
Each mechanical coupling segment comprises a housing having projections which extend radially inwardly from the housing and engage, for example, the outer surfaces of plain end pipe elements, pipe elements having a shoulder and bead, or circumferential grooves that extend around each of the pipe elements to be joined. Engagement between the projections and the pipe elements provides mechanical restraint to the joint and ensures that the pipe elements remain coupled even under high internal pressure and external forces. The housings define an annular channel or pocket that receives a ring gasket or seal, typically an elastomeric ring which engages the ends of each pipe element and cooperates with the segments and the pipe elements to provide a fluid tight seal. The segments have connection members, typically in the form of lugs which project outwardly from the housings. The lugs are adapted to receive fasteners, such as nuts and bolts, which are adjustably tightenable to draw the segments toward one another.
The projections on prior art couplings typically have arcuate surfaces with a radius of curvature that is substantially matched to the radius of curvature of the outer surface of the pipe element that it is intended to engage. For couplings used with grooved pipe elements, the radii of curvature of the arcuate surfaces are smaller than the radii of curvature of the outer surfaces of the pipe elements outside of the grooves so that the projections fit within and engage the grooves.
Methods of securing pipe elements in end to end relation comprise a sequential installation process when mechanical couplings according to the prior art are used. Typically, the coupling is received by the technician with the segments bolted together and the ring gasket captured within the segments' channels. The technician first disassembles the coupling by unbolting it, removes the ring gasket, lubricates it (if not pre-lubricated) and places it around the ends of the pipe elements to be joined. Installation of the ring gasket often requires that it be lubricated and stretched to accommodate the pipe elements. With the ring gasket in place on both pipe elements, the segments are then placed one at a time straddling the ends of the pipe elements and capturing the ring gasket against them. During placement, the segments engage the gasket, the projections are aligned with the grooves, the bolts are inserted through the lugs, the nuts are threaded onto the bolts and tightened, drawing the coupling segments toward one another, compressing the gasket and engaging the projections within the grooves.
As evident from the previous description, installation of mechanical pipe couplings according to the prior art requires that the technician typically handle at least seven individual piece parts (and more when the coupling has more than two segments), and must totally disassemble and reassemble the coupling. Significant time, effort and expense would be saved if the technician could install a mechanical pipe coupling without first totally disassembling it and then reassembling it, piece by piece.
FIG. 1 shows a coupling 11 having coupling segments 13 and 15. The segments are joined end to end by connection members 17 and 19, the connection members including threaded fasteners 21. The segments 13 and 15 are shown supported in spaced relation from one another on the outer surface of the ring gasket 23 captured between the segments. This configuration is possible because the circumference of the outer surface of an undeformed ring gasket 23 is greater than the sum of the circumferences of the surfaces on the segments with which the ring gasket outer surface interfaces. When the segments are supported in this manner it is possible to insert pipe elements into the central space 25 between the segments without disassembling the coupling. However, there are some drawbacks to this solution to the problem of installing mechanical couplings. Note in particular that the ring gasket 23 is distorted into an oval shape by the geometry of a close-fitting segment riding on at least a portion of the ring gasket before the gasket has properly seated in the gasket pocket of the segment. If the degree of distortion of the ring gasket is uncontrolled, the oval shape can result in pinching and damage to the gasket in the region between the connection members 17 and 19 of the segments 13 and 15.
There is clearly a need for a pipe coupling with which the distortion of the ring seal may be controlled so as to avoid damage to the ring seal with which it is used, yet will also allow pipe elements to be inserted reliably without disassembly of the coupling.